The present invention relates to high-performance liquid chromatography (HPLC) coupled directly with capillary gas chromatography (GC). More particularly, the invention is directed to a method and apparatus for on-line coupling of liquid and gas chromatography columns in which there is direct quantitative transfer of sample from a liquid chromatography analytical column to a gas chromatography column.
The transfer of a selected fraction from a liquid chromatograph into a gas chromatograph has been reported; however, analyses were performed either off-line, requiring collection and re-injection of the separate fraction (e.g., F. DeSanzo, et al., Anal. Chem. 52 (1980) 906), or on-line, using conventional high performance liquid chromatography columns, whereby only a fraction of the separated peak (nonquantitative analysis) or a well resolved component (limited quantitative analysis) could be transferred into a gas chromatograph (e.g., J. Apffel, H. McNair, J. Chromatogr. 279 (1983) 139: K. Grob, Jr., et al., J. Chromatogr. 285 (1984) 55).
Apffel and McNair used an ordinary GC autosampler as an interface between an HPLC detector and the gas chromatograph. The effluent from the HPLC column was routed through the syringe of the autosampler to waste. The liquid flowing through the syringe was analyzed by the injection of a few microliters into a vaporizing injector. This technique did not provide a direct LC-GC coupling as desired, however, due to the very small amount of liquid that could be successfully introduced into the GC system.
K. Grob, Jr., et al. employed a "retention gap" (typically an inlet having low or negligible retention compared to the gas chromatography stationary phase) in an on-column injection mode to transfer large volumes of liquid directly from an HPLC column to a GC column. However, no suggestion is given in this reference of simultaneously vaporizing the solvent (liquid chromatography mobile phase) as it is being transferred into the retention gap. In contrast, the teaching requires the formation of a flooded zone (30-100 meters) of liquid in the retention gap. Additionally, in all of the specific examples, precise temperature control insures that the retention gap is maintained at a temperature below the boiling point of the solvent until the solvent peak has passed through the GC column.